//calc design size
@function baseFontSize($width) {
  @return 20 * $width / 640;
}
// pixels to rems 
@function pxToRem($px) {
  @return $px / $baseFontSize / 2 * 1rem;
}
//abbr pxToRem
@function rem($px) {
  @return $px / $baseFontSize / 2 * 1rem;
}